I have 3 choices for Audio out, “Built-in”, “HDMI”, and “Scarlet Solo USB”. If I choose Built-in or Scarlet Solo USB, it can play to either of those fine, but if I choose HDMI, I get the following message:
Error opening sound device. Try changing the audio host, playback device and the project sample rate.
I’ve tried a number of different sampling rates, none make any difference.
I am using Audacity 2.1.3 on Mac OSX 10.12.5 (Sierra).
My HDMI is connected to an Insignia NS-24E350A13 Firmware Version V2.02
Wikipedia has this to say. Not all that helpful because they don’t say what the baseline format actually is.
For digital audio, if an HDMI device has audio, it is required to implement the baseline format: stereo (uncompressed) PCM. Other formats are optional, with HDMI allowing up to 8 channels of uncompressed audio at sample sizes of 16-bit, 20-bit and 24-bit, with sample rates of 32 kHz, 44.1 kHz, 48 kHz, 88.2 kHz, 96 kHz, 176.4 kHz and 192 kHz.6 HDMI also carries any IEC 61937-compliant compressed audio stream, such as Dolby Digital and DTS, and up to 8 channels of one-bit DSD audio (used on Super Audio CDs) at rates up to four times that of Super Audio CD.6
I was able to get it to work by closing Audacity and reopening it…but after my Mac went into sleep mode, it failed again until I closed Audacity and reopened it.
When your Mac goes to sleep, the HDMI device probably shuts down. When your machine wakes up and the HDMI device restarts, it is effectively a “new” device, so Audacity does not recognise it.
One solution, as you have found, is to restart Audacity.
Another solution that will ‘probably’ work, is to “Rescan audio devices” from Audacity’s “Transport” menu.